There is a need for a new and more intuitive method for analyzing the external field of view afforded pilots by the windows on the flight deck of an aircraft. The external field of view created by an airliner's flight deck windows must satisfy many regulatory and design requirements intended to insure that the view is adequate for the pilots to operate the aircraft safely and gives them a reasonable opportunity to see and avoid other aircraft that pose a collision threat.
The external visual field can be evaluated using “polar projections,” which are angle-angle plots of the limits of the solid angle that the pilots can see out of the windows. The polar projection is a two dimensional curve that specifies combinations of left/right angles (azimuth) and up/down angles (altitude) measured from the line straight forward from the pilots' eyes. Those azimuth and altitude combinations represent the limits of the pilot's field of view out of the windows.
During the design process, proposed window designs can be evaluated by comparing the polar projection of the proposal against the polar projection of previous designs and against the regulatory requirements, expressed in angle/angle coordinates.
Polar projections for proposed window designs may be obtained by constructing sight rays from certain design eye positions or eye reference points in the cockpit to the edges of the windows. Calculating and plotting the polar projection for a window design in this manner is not a straight-forward geometric construction, however, due to the following factors. Both left and right eyes of the pilot are involved. The final graph is a union of the vision from both eyes. The pilots head is rotated as the window area is scanned; therefore the origin point for each sight ray is continuously changing. Also, the sight rays are refracted as they pass through the transparency material.
A polar projection is created by scanning visual edges that create the limits of the view out of the windows. These edges could be the edges of the window frame or the linings and the equipment inside the flight deck. The complete graph is created by scanning all the relevant edges and projecting them on a 2D angle-angle graph using the concepts noted above. This may be done for the left and right eye and the projected areas are combined to create an “ambinocular vision polar.”
Previously, aircraft manufacturers used internally developed software programs to calculate and draw vision polars. This software ran on obsolete operating systems using an obsolete database program, and the software itself was poorly documented and difficult to validate. The input data consisted of coordinates for points along window edges and liners, and the output was a polar projection that could be printed or pasted into a word processor, but could not be used in a CAD program.
The old software was not interactive, not resident in a CAD program, and not available to a designer actually designing window opening shapes; therefore, it was not useful as a design tool.